1. Field of the Invention
The present invention relates to a liquid applying apparatus and an ink jet printing apparatus, and particularly to a liquid applying apparatus that applies a liquid to a medium for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials. Likewise, the present invention relates to an ink jet printing apparatus including a mechanism that applies the liquid to a print medium used for ink jet printing, for a purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials.
2. Description of the Related Art
A spin coater, a roll coater, a bar coater, and a die coater are known as systems for applying a liquid or an aqueous material to various media. These applying systems are premised on continuous application on relatively long applying media. Thus, for example, if liquid is applied to applying media having a relatively small size and intermittently conveyed, for each applying medium, paint beads may be disturbed at a position at which applying is started or ended. In this case, the coats obtained may be non-uniform among the applying media.
A known configuration that can solve this problem is described in Japanese Patent Laid-Open No. 2001-70858. On the basis of the die coater system, this configuration uses a rotating rod bar and ejects paint to the rod bar through an ejection slit to form a coat on the rod bar. The coat formed is contacted with and transferred to an applying medium as the rod bar rotates. In this case, if the coat formed on the rod bar is not transferred or applied to the applying medium, the paint is returned to a head by the rotation of the rod bar. The paint is then collected via a collecting slit. In other words, the rod bar continues to rotate even during non-applying, while the paint is being formed into a coat on the rod bar. This enables a uniform coat to be obtained even if applying media are intermittently supplied and being applied with the paint.
Even in the field of ink jet printing apparatuses, those using a liquid applying mechanism are known. Japanese Patent Laid-Open No. 2002-517341 describes an apparatus which uses a blade contacting with a roller and in which the coating liquid is collected between the blade and the roller so that the coating liquid is applied to the roller as the roller rotates. As the roller rotates, the coating liquid is transferred and applied to a support conveyed between this roller and another roller. Japanese Patent Laid-Open No. 08-72227 similarly discloses a mechanism in an ink jet printing apparatus which applies a treatment liquid before printing which insolubilizes dyes.
However, with the configurations described in the above patent documents, an application liquid is applied or supplied to the surface of the rod bar or roller, while the rod bar or roller rotates. However, the part of the rod bar or roller to which the application liquid is applied or supplied is open to or in communication with the air. Thus, disadvantageously, the application liquid may be evaporated or for example, the application liquid may leak when the posture of the apparatus is changed.
In particular, with an ink jet printing apparatus such as a printer, in view of, for example, the leakage of the liquid caused by a change in the posture of the apparatus during transportation thereof, it is difficult to apply the applying mechanism described in the above documents to the apparatus of which the size has been reduced.
In contrast, Japanese Patent Laid-Open No. 08-58069 discloses a configuration that seals a part that applies or supplies ink, that is, application liquids, to a roller. The applying mechanism described in this document operates in a gravure printing apparatus to apply ink to an applying roller having the surface of which is formed with a pattern of a printing plate. This mechanism uses an ink chamber (liquid holding member) having blades arranged at two vertical positions along a peripheral surface of the applying roller and extending in a longitudinal direction of the applying roller, and elastic members provided at both sides of the two blades. The chamber (liquid holding member) is contacted with the peripheral surface (applying surface) of the applying roller to form a liquid chamber between the ink chamber and the applying roller. Then, the applying roller is rotated to apply or supply the application liquid from the liquid chamber to the applying roller.
However, in the event of applying the technology disclosed in Japanese Patent Laid-Open No. 08-58069 to an apparatus for applying an applying liquid uniformly to an applying medium through an applying roller, the transferring capability of the applying liquid to the applying medium and the sealing capability are insufficient. In other words, with Japanese Patent Laid-Open No. 08-58069 which discloses gravure printing technology, a convex-concave pattern is formed on the surface of the applying roller, and the transfer amount of the applying liquid to the applying medium is not uniform, so that transferring capability cannot be sufficient. Also, the convex-concave pattern formed on the surface of the applying roller results in insufficient sealing by the contacting of the applying roller and the liquid holding member (ink chamber). Further, the material of the applying roller surface being metallic also is a cause of insufficient sealing.
The results of study by the present inventor indicate that in order to have both transferring capability of the applying liquid to the applying medium and sealing capability, the surface of the applying roller is desirable to be configured with an elastic member, and further is desirable to have as soft a material as possible. Further, the desirable hardness of the elastic member for the surface of the applying roller is less than a rubber hardness of 40 degrees.
Therefore, the surface of the applying roller was configured with an elastic member and further investigation was continued. Then the following new problem occurred. First, an apparatus was prepared having an applying member such as an applying roller having an applying surface made of an elastic surface and a liquid holding member that abuts against the applying surface to form a liquid holding space to hold the liquid, and this apparatus was stopped for a long period of time. That is to say, the apparatus was allowed to stand for a long period of time without changing the contact position of the applying surface and the liquid holding space. Then pressure was formed on the contacting part of the liquid holding member on the applying surface, and the applying surface of the parts thereof was distorted. Whatever type of rubber material is used, this distortion is not removed instantaneously even when the pressure is released. If the apparatus is stopped for a long period of time and is subsequently started an applying operation, the applying surface having the concave portion generated in the contact part applies the applying liquid to the medium. The concave part of the applying surface generates a state of the applying surface and the applying medium not contacting, or a state wherein contact between the applying surface and the applying medium is small. Thus, the applying liquid may not be applied on portions of the applying medium, or insufficient applying liquid is applied.